And he seized on the plummeting price of oil over the last year as proof an independent Scotland would have been forced to endure years of pain because of dwindling revenues from the North Sea.

He also cited the Greek crisis in the eurozone as further evidence that Salmond’s flagship currency policy to keep the pound was a pipe dream.

Darling, 61, stepped down as the MP for Edinburgh South West in May and has recently been appointed to a new role in the House of Lords.

Darling speaks with David Clegg (Image: Paul Chappells/Daily Record)

But in Scotland, his political career will always be remembered for uniting Labour, Tories and the Lib Dems under the Better Together banner in order to defeat the nationalists.

Quizzed on whether he has any regrets about the campaign, Darling is reluctant to put his finger on anything in particular.

He said: “There has never been a campaign in history where you can’t look back and say you wouldn’t have done things differently. But at the end of the day we won and won decisively.

“And if you had the referendum again tomorrow morning we would still win by that margin.

“I think the reason we would win, which Nicola Sturgeon has been candid enough to admit, is that they couldn’t make a convincing economic case.”

Darling remains confident of that position, despite an Ipsos Mori poll published by STV at the beginning of September finding 53 per cent of respondents now in favour of a Yes vote. It also indicated that the Nationalists would win next May’s Holyrood election with 74 seats.

Yet, Darling is unfazed. He says even when a YouGov poll 10 days before the September 18 referendum sensationally put the Yes side ahead, he never doubted the two-and-a-half year campaign would end in a No vote.

He said: “My reaction then was that it would give them a lift and in any campaign, momentum matters.

“I knew it would be close but I just had this instinct all along that we would win. I remember when I was going to the count on polling day somebody asked what I would do if we didn’t win and I said we WERE going to win.

“Our pollster – who was very good – had said the gap would narrow rapidly because the people who are going to go with their hearts declare before people who are going with their heads and that’s what happened.”

Darling also rubbished the idea that Better Together – who quickly won the nickname Project Fear for raising a host of concerns about the prospect of ­independence – were too negative.

He said: “I completely refute that. I was told it was negative to say that oil prices might come down. Yet we were told it was going to be $113 a barrel and it is now half that and nobody seriously expects it to recover anytime soon.

“I was told it was negative when I was asked where the legal advice was that said we would automatically get into the European Union and it turned out it didn’t actually exist.

“The more they said we were being negative, the more I thought they had something to hide.”

Darling revealed that he bumped into Salmond a few months ago in a London hotel and the pair exchanged pleasantries in a “civil manner”. But the Labour man said he has not read the former first minister’s best-selling referendum diary and doesn’t have much time for his behaviour since the vote.

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Darling said: “It is entirely predictable – like most of his life – it’s not his fault, it’s somebody else’s.”

He is also concerned that the divisions caused by the referendum are still festering.

He added: “That’s what worries me. There’s still a lot of division about.

“I don’t have any problem with someone who passionately takes a different view to the one I take but we need to be tolerant of each other.

“What worries me is that the longer you keep this going, the deeper these divisions become.

“We are a small country, we need to work together. That is why the idea of a ‘neverendum’ will fill many people with despair.

“Because every time you are discussing that, you are not discussing what matters, like the quality of teaching in schools or what is going on with policing in Scotland at the moment.”

Despite that legacy, Darling is still convinced he was right to take the pro-Union stand and shudders at the thought of what would have happened if there had been a Yes vote last year.

He said: “In crude terms we would be facing the fact we were spending £10billion more a year than we are getting in.

“And with oil going down you would be facing a very uncertain and difficult future. Of course, you could deal with it but there would be a lot of pain.”